#Prokaryote vs Eukaryote

#Endosymbiosis

#Eukaryote Reproduction

#A.O.G.

• All Eukaryotes are protists except plants, animals and fungi
  • mostly unicellular
  • several ‘supergroups’

• Extraordinarily diverse

  • 60,000 species described

  • autotrophs, heterotrophs, or mixotrophs
  • asexual or sexual reproduction
  • functions carried out by organelles
  • membrane bound nucleus

• First undisputed fossils ~1.8 bya
  • spherical algal protists
  • many protists do not make fossils
  • common ancestry unresolved

Single-celled does not = simple for Eukaryotes. Protists can have very elaborate cells

We do not know whether nucleus or organelles occurred first!

• Mitochondria and chloroplasts are about the size of an average bacterium

• Both organelles replicate independently by fission, as do bacteria
  • have their own ribosomes to make their own proteins
  • mitochondria/chloroplasts each have a circular chromosome

• Both organelles have double membranes consistent with the engulfing mechanism

• Genes of each organelle closely resemble ancestors!
  • cyanobacteria for chloroplasts
  • proteobacteria for mitrochondria
  • some genes have shifted from bacteria to host, possibly explaining why ‘mitochondria’ are not free-living

• Algae ingested by other heterotrophic eukaryotes!
  • led to Euglenoids, Diatoms and Brown algae

• Chloroplasts transferred to other protists
  • results in chloroplasts not from common ancestor!

• How do we know this happened?
  • HINT: # of membranes around organelles = ____

• Haplonic life cycles: most life spent with one set of chromosomes (1N)
  • all cells are haploid (some multi-cellular algae, and fungi)
  • zygote only diploid cell → meiosis into daughter cells

• Diplonic life cycles: most life with pairs of chromosomes (2N)
  • body cells (e.g., animals) are all diploid
  • sex cells (gametes) are haploid via meiosis → then fuse

• Asexual life cycles: binary fission
  • nucleus divides, then cell divides into two separate organisms → mitosis
  • many-single celled protists can switch to asexual reproduction

• There are more….
  • parasites require hosts

• More complex life cycles include an alternation of generations
  • some algae and plants
  • both generations must be multi-cellular

• AOG = the alternation of multi-cellular haploid and diploid generations
  • diploid (2N) = sporophyte → makes spores
  • haploid (1N) = gametophyte → male/female → make gametes
  • fertilization of gametes makes new sporophyte

• In some species the different generations look similar while in others they look different